1. Field of the Invention
The invention relates to an infinitely variable ring gear pump comprising a stationary casing, an internal rotor in the casing rotatably supported and driven by means of a shaft and an external rotor likewise rotatably supported, meshing with the internal rotor, the difference in the number of teeth of the gear ring running set comprising the internal rotor and the external rotor being equal to unity, having a tooth shape in which a plurality of expanding and contracting displacement cells each sealed off from the other materialize, due to tooth tip contact and kidney-shaped low and high pressure ports fixedly arranged laterally in the region of the displacement cells being provided in the casing, the ports being separated from each other by webs and the angular position of the eccentric axis (eccentricity) of the ring gear running set being variable relative to the casing, wherein the support or bearing of the external rotor of the ring gear running set occurs at an outer diameter of the latter in an adjusting ring preferably the same in width which is rollable with zero slip by its outer circumferential or pitch circle on an inner circumferential or pitch circle and the difference in the diameters of the two circumferential or pitch circles equals twice the eccentricity of the ring gear running set. The specific delivery (displacement/speed) of the variable ring gear pump in accordance with the invention can be varied.
2. Description of the Prior Art
Known gear pumps feature a specific delivery which is constant due to the system involved, because the geometry of the displacement "cells" cannot be varied. The expanding and contracting displacement cells fluctuate during rotation of the gear set from a minimum to a maximum and back to a minimum, because the teeth are rigid and non-variable. This constancy in the specific delivery automatically results in the delivery of the pump being proportional to its rotary speed as long as the displacement cells are filled 100%.
However, in many applications this proportionality is a nuisance and undesirable. Although in a press, for instance, a high hydraulic fluid delivery is necessary for the rapid advance, whereas in the final phase of the working stroke only high pressure is still delivered, the hydraulic fluid delivery requirement drops to zero. Since the drive speed of such pumps as a rule remains constant, excess delivery materializes at high pressure which is returned to the fluid reservoir with a loss in energy.
This excess delivery is particularly a nuisance, for example, in the case of engine lubricating pumps on motor vehicles and in the case of oil supply pumps on automatic transmissions. Although these require at low engine speed and thus lower pump speeds a minimum delivery needed for idling and a minimum oil pressure at high speeds, the oil flow required at higher speeds is way below the proportionality line, however, it being mostly less than a third of the proportionality flow at maximum speeds.
Aside from the many efforts made in solving this problem by suction throttling, solutions involving variable vane-type pumps have been proposed. Also known are solutions involving two-register pumps for achieving at least two delivery stages or involving two running sets operating variable relative to each other.
One good approach to solving the problem is a ring gear pump as an internal gear pump requiring no crescent due to the gear shape being selected so that by tooth tip contact each tooth chamber is reliably sealed off from the adjacent tooth chambers so that a good volumetric efficiency is achieved. In such ring gear pumps there is the possibility of varying the axial spacing of the internal rotor from the external rotor or the angular location of the eccentric axis relative to the casing and thus relative to the supply and discharge ports in the casing.
One design solution could consist of supporting or bearing the external rotor in a cam ring rotatably arranged variable in the casing. For near zero adjustment of delivery needed in practical application as is highly desirable in cold starting, a 90.degree. angular adjustment of the cam or eccentric axis is needed. This means that the cam ring for adjusting the eccentric axis of the running set needs to be turned through 90.degree. and thus over a large perimeter, this in turn requiring a very large travel of the governor spring which would result in dimensions which are very difficult to achieve due to the necessary soft spring characteristic. Since especially in the case of motor vehicle engines and automatic transmissions very frequent and fast changes in speed occur, the cam ring would have to experience high rotary accelerations and delays which would result in high adjusting forces, high resistance thereto and high wear. Also, the risk of soilage of the large governing spaces is high.